Oxidizing agent



United State Patent. l. 1

of fuming nitric acid.

The effect of sodium nitrite and water on the freezing point of pure nitric acid is shown in the following Table I:

TABLE I OXIDIZING. AGENT 5 viiifiiii" 59mm, 1 Millilllel Al.l lzjino, Berkeleyg (jall ifi, assignig California Percent) gi esearc 0 oration an rancisco a co 0- i ration of Delz i v vare i fi Water 1 Percent) No Drawin A licationlune 20 1952 Serial No. 294,726, x {8g 3 g :23, 2 Claims. (Cl. 252-186) 1-58 3 Z :23 .99 r 0 --44- 99 1 4. --65. 9s 2 0 48' This invention relates to an oxidizing, agent containing 8g f :gg nitric acid as the essential oxidizing component and char- 97' a 0 52 acterized by a low freezing point and'high stability. g; i g :2; Hypergolic fuels for use in thrust engines ordinarily 96 4 4 97 contain two components: a reducing component which is an organic compound, and nitric acid which is the oxidizing component. Upon mixing of the two com- It will benoted that when water and sodiumv nitrite ponents, spontaneous ignition occursand the ejection of are both added to nitric acid; the freezing point lowering the-gaseous products of combustion from the engine, proobtained is greater than the sum of the freezi'ngjpoint vide the desired thrust. White fuming nitric acid is com.- lowerings' obtained by adding these, materials separately monly employed as the oxidizing'component of such to nitric acid; for example, 2% by weight ofwater lowers fuels. the freezing point 8 Fahrenheit degrees; 2% by weight Nitric acid has two disadvantages in'this area of use. of sodium nitrite lowers the freezing; point of the nitric First, nitric acid tends to decompose on storage accordacid by 8 Fahrenheit degrees; but 2% by weight of water ing to the reaction: and 2% by weight of sodium nitrite lower the freezing point by 23 Fahrenheit degrees. Similarly, 4% by weight 4HNO3+ 4NO2+ 2H2O+ O2 of water lowers the freezing-point of nitric acid 17 Fahren- Over a period of time gas pressures build up in the storage r heit degrees; 4% y Weight of sodium nitrite lowers the vessels to a point which may constitute a serious hazard. freezing Point y 19 Phhfehheit degrees; t 4% y Secondly, white fuming nitric acid has a relatively high Weight of Water a 4% y Weight of sodiumtflih'ite lower freezing point, about 40 F. In jet powered aircraft, the freezing: Point y nearly 60 Fahrefl'heiii g e operated at high altitudes, this relatively hi'gh'freezing From the i of freezing-Point, y desirable point constitutes a serious operating disadvantage: The Position is one that Contains 3 to P y Weight of nitric acid may freeze either in the storage tanks or in i sodium nitrite and 2 t0 4 Paris y Weight Water to the lines connecting the storage tank to the combustion each 100 Parts by Weight of HNO3- chambers f h thrust engines, 40 The storage stability of nitric acid, of nitricacid con- Nitric id would b much better adapted to use i taining sodium. nitrite, and 05 nitric acid containing sothrust engines of aircraft if its storage stability could dum nitrite and wa r has n edl Nitric a be increased and its freezing point lowered. The probdecomposes n storage, forming nitrogen dioiiide, ylem of accomplishing these ends is further complicated gen, and stabiliiiy is deieffhiiled y ieeileeiihg by the fact that the ignition delay of the mixture of the Oxygen l ased frorrlnitric acith held at a temperanitric acid with the organic component of the hypergolic 'e 9 a given Period of time- Prior t0 fuel must not be materially increased as one seeks to iniilahhg the eell'eetloh, sample of nitric improve the stability and reduce the freezing point of held is frozen y immersion in a bath of solid Carbon the nitric id dioxide and acetone. The gas collection system is then It is an object of this invention to provide a nitric acid 50 evacuated and held under a vacuum for abmlt One-half I oxidizing composition which is stable on storage, which hour to de'gas e acid- At the end of about One-half has a very low freezing point, and whi h ha a h t hour, helium is 1ntroduced into the system to restore ignition delay when mixed with suitable organic comatmosPhelic Pressure The acid sample is then melted pounds to constitute a hypergolic f l and placed in a constant temperature bath maintained It has been found that fuming nitric acid is materially at The gas formed y decomposition of the improved in respect to its storage stability and freezing acid is Passed through a tube Packed With g point by the addition to the nitric acid of a small amount strongly basic matel'lal Whlch absorbs nitrogen dioxide of sodium nitrite and a small amount of water. The i'e so that y the Oxygen formed in the quantities of sodium nitrite and water employed are each Position is collected and measured; each mole of in the range from 1 to 5 parts by weight per parts 6 Oxygen collected, 4 moles of nitric acid have decomposed. The following Table II shows the volume of oxygen collected at various time intervals from the decomposition of white fuming nitric acid, white fuming nitric acid containing sodium nitrite, and from white fuming nitric acid containing sodium nitrite and water.

TABLE II Gas volume in cc.

positions containing 96 parts by weight of 96% I-INOa 1 N gas was evolved during 48 hours at 122 F. 7

It will be noted that the rate of decomposition is considerably reduced by the, presence of sodium nitrite and that when both sodium nitrite and water were present in the acid, no decomposition occurred during a 48 hour test period.

The data presented above indicates the effectiveness of sodium nitrite and water to lower the freezing point of fuming nitric acid and to stabilize it. These results are obtained without seriously increasing the ignition delay period of most hypergolic fuels which use nitric acid as the oxidizing component. An ignition delay period of about 50 milliseconds may be arbitrarily set as a practical working maximum. If the ignition delay period is appreciably longer, the amount of the hypergolic fuel mixture which is injected into the combustion chamber of a thrust engine before ignition occurs may be so large that when the body of hypergolic fuel finally does ignite, an explosive force may be exerted which may damage the combustion chamber.

Ignition delays were measured using a mixture of diallyl sulfide and diallyl aniline as the reducing component of the hypergolic fuel and using white fuming nitric acid containing varying amounts of water and/or sodium nitrite as the oxidizing component. Ignition delays for these hypergolic mixtures at; 40 F. are set out in the following Table III in milliseconds:

TABLE III Composition of W N (W t. Sodium Corrected Percent) Nitrite in Average W FNA Ignition (W t. Per- Delay Nitric Water cent) (Ms.)

Acid

and 4 parts by weight of sodium nitrite have an ignition delay period of 52 milliseconds, which is a safe value. It will be noted that a mixture of 96 parts by weight of HNOa and 4 parts by weight of water containing no sodium nitrite has an ignition delay period of 80 milliy seconds, which is high.

While only sodium nitrite has been exemplified above, the other alkali metal nitrites may be substituted for sodium nitrite; they are, however, generally more expensive and less eflective than sodium nitrite.

I claim:

1. A stable oxidizing agent having a low freezing point consisting essentially of nitric acid, sodium nitrite and water, (the amounts of sodium nitrite and water being each at least 1 part by weight and not more than 5 parts by weight to'lOO parts by weight of nitric acid.

2. A stable oxidizing agent having a low freezing point consisting essentially of nitric acid, sodium nitrite and water, the parts by weight of sodium nitrite and water per parts by weight of nitric acid being in the ranges 2 to 5 and 2 to 4, respectively.

References Cited in the file of this patent UNITED STATES PATENTS 1,506,323 ONeill Aug. 26, 1924 2,403,932 Lawson July 16, 1946 2,573,471 Malina et a1. Oct. 30, 1951 OTHER REFERENCES Scoville: Art of Compounding, Blakiston, 5th Ed. (1927), pp. 434-439.

Killefierz- Fuels for Jets, Scientific American (September 1945), pp. 162-164.

From the table it will be noted that nitric acid com- 

1. A STABLE OXIDIZING AGENT HAVING A LOW FREEZING POINT CONSISTING ESSENTIALLY OF NITRIC ACID, SODIUM NITRITE AND WATER, THE AMOUNTS OF SODIUM NITRITE AND WATER BEING EACH AT LEAST 1 PART BY WEIGHT AND NOT MORE THAN 5 PARTS BY WEIGHT TO 100 PARTS BY WEIGHT OF NITRIC ACID. 